1. Field of the Invention
The present invention generally relates to an optical apparatus and a method for producing the same. Specifically, the present invention relates to a light generator including a semiconductor laser and a waveguide type optical function device, and a method for producing the same. The present invention also relates to an oscillation wavelength stabilizer for a light source such as a semiconductor laser having a distributed Bragg-reflector (DBR) region, a harmonic output stabilizer for a short wavelength light source which includes a semiconductor laser having a DBR region and a wavelength converting device, and further to an optical disk system including the same.
The entire disclosure of U.S. patent application Ser. No. 09/480,217 filed Jan. 10, 2000 is expressly incorporated by reference herein.
2. Description of the Related Art
In the optical information processing field, optical functional devices for modulating light output from a semiconductor laser at high speeds or halving the wavelength of laser light have been vigorously developed. In particular, waveguide type optical functional devices are promising for realizing the modulation of laser light at a frequency of several gigahertz or more or obtaining 1 mW or more of short-wavelength laser light. Hereinbelow, a waveguide type second harmonic generation (SHG) device (Mizuuchi et al., IEEE, Journal of Quantum Electronics, 30 (1994), pp. 1596) and an optical modulation device will be briefly described.
A typical SHG device 50 will be explained referring to FIG. 16, which is a perspective view of the SHG device 50.
The SHG device 50 includes a z-cut LiTaO3 crystal substrate 31. A waveguide 32 and periodical domain inverted regions 33 extending perpendicular to the waveguide 32 are formed on the z-cut LiTaO3 crystal substrate 31. The SHG device 50 allows harmonics to be generated with high efficiency by compensating the unmatching of the propagation constant between a fundamental wave and a generated harmonic with the periodical structure of the domain inverted regions 33.
Such an SHG device 50 is fabricated in the following manner.
A Ta electrode pattern is formed on the z-cut LiTaO3 crystal substrate 31 (made of nonlinear optical crystal) by evaporation and photolithography having a periodic spacing of several micrometers. A voltage of 2 kV/mm is then applied to the resultant substrate to form the periodic domain inverted regions 33. Thereafter, a stripe made of Ta, extending perpendicular to the periodic domain inverted regions 33, is formed on the substrate. The resultant substrate is heat-treated with pyrophosphoric acid for about 16 minutes, subjected to proton exchange, and annealed at about 420xc2x0 C. for about one minute, to form the waveguide 32.
The proton-exchanged waveguide 32 allows only light having a polarized component in the z direction to propagate therethrough. In general, the SHG device using the z-cut LiTaO3 crystal substrate has a higher conversion efficiency into a harmonic, though the SHG device can also be fabricated using an x-cut LiTaO3 crystal substrate.
A conventional light generator including such a waveguide type SHG device and a semiconductor laser will now be described.
Referring to FIG. 17, light emitted from a semiconductor laser 34 is guided into a waveguide 40 having a waveguide type SHG device 39 via two coupling lenses 35 and 38. More specifically, light emitted from a semiconductor laser 34 is collimated by a collimator lens 35, passes through a half-wave plate 36 and a bandpass filter 37, and is focused on the waveguide 40 of the waveguide type SHG device 39 by a focusing lens 38. The semiconductor laser 34 oscillates at a TE mode, while the waveguide 40 allows only a light component polarized in the z direction to propagate therethrough. The half-wave plate 36 is used to obtain the maximum overlap between the light emitted from the semiconductor laser 34 and the light propagating through the waveguide 40. The laser light emitted from the semiconductor laser 34 is converted into harmonic light while propagating in the waveguide 40 and output from the emergent end face thereof.
This conventional light generator generates about a 2.8 mW blue light with a wavelength of 430 nm from 120 mW laser light with a wavelength of 860 nm emitted from an AlGaAs semiconductor laser as the fundamental wave. The module volume of this light generator using the above two coupling lenses 35 and 38 is about 3 cc (Kitaoka et al, the review of laser engineering, 23 (1995), pp. 787).
As optical disk systems and optical communication systems have been generally and widely used, demands for reducing the size and cost of relevant components have increased. In order to reduce the size and cost of the light generator including the semiconductor laser and the waveguide type optical functional device, it is required to simplify the optical coupling adjustment (i.e., the alignment adjustment for obtaining the optical coupling) and omit any coupling lens. In the conventional module structure, as shown in FIG. 17, using two coupling lenses 35 and 38 for guiding laser light of the semiconductor laser 34 to the waveguide 40, there are required four axial adjustments: i.e., adjustments of the focusing lens 38 and the collimator lens 35 both along the optical axis (direction y in FIG. 17); and adjustments of the semiconductor laser 34 in directions x and z in FIG. 17. Thus, a certain period of time is required for realizing the adjustment, and fabrication cost is increased. Further, the module structure including two coupling lenses has a relatively large volume of about 3 cc and occupies a relatively large space. The time and cost required for the optical coupling adjustment and the module volume of about 3 cc of the conventional optical functional device are disadvantageous in the application of the device to consumer appliances such as optical disk systems.
A direct-coupling module including no coupling lens has been proposed to achieve size reduction (Japanese Patent Publication No. 5-29892). This type of module, however, still requires alignment adjustments for optical coupling along two or three axes, requiring time and cost for the optical coupling.
Another problem of the conventional light generator is that presently it is difficult to optically couple the waveguide formed on the z-cut crystal substrate by proton exchange and the semiconductor laser light oscillating at the TE mode on one submount in a simple manner. The waveguide formed on the z-cut crystal substrate by proton exchange allows only light of a TM mode to propagate therethrough. Therefore, a half-wave plate is required to mount both the waveguide and the semiconductor laser emitting light of a TE mode on one submount.
By the way, optical disk systems using a near infrared semiconductor laser with a wavelength of a 780 nm band or a red semiconductor laser with a wavelength of 670 nm have been vigorously developed. In order to enhance the density of an optical disk, It is required to reproduce smaller spots. To reproduce smaller spots, a higher numerical aperture (NA) of a focusing lens and a shorter-wavelength of a light source are required. One of the conventional techniques for shortening the wavelength is second harmonic generation (SHG), where a near infrared semiconductor laser and a domain inverted type waveguide device of a quasi-phase matching (QPM) method is used (see Yamamoto et al., Optics Letters, Vol. 16, No. 15, 1156 (1991)).
FIG. 34 is a schematic structural view of a blue light source using a domain inverted type waveguide device (the SHG blue laser).
Referring to FIG. 34, the light source includes a 0.85 xcexcm-band, 100 mw-class AlGaAs DBR semiconductor laser 123, a collimator lens 124 with an NA of 0.5, a half-wave plate 125, a focusing lens 126 with an NA of 0.5, and a domain inverted type waveguide device 127. The DBR semiconductor laser 123 includes a DBR region for fixing the oscillation wavelength. The DBR region has an internal heater for varying the oscillation wavelength. The domain inverted type waveguide device 127 includes a waveguide 129 and periodic domain inverted regions 130 formed on an LiTaO3 substrate 128. The polarized direction of laser light collimated by the collimator lens 124 is rotated by the half-wave plate 125, and the resultant light is focused on the incident end face of the waveguide 129 of the domain inverted type waveguide device 127. The focused light propagates through the waveguide 129 having the domain inverted regions 130, to be output from the emergent end face of the waveguide 129 as a harmonic and a non-converted fundamental wave.
In the domain inverted type waveguide device 127, the phase-matching wavelength allowance where high efficiency wavelength conversion is possible is as narrow as 0.1 nm. To overcome this problem, the current amount supplied to the DBR region of the DBR semiconductor laser 123 is controlled, to fix the oscillation wavelength within the phase-matching wavelength allowance of the domain inverted type waveguide device 127. As a result, typically, about a 3 mW blue light with a wavelength of 425 nm is obtained for 70 mW laser light incident on the waveguide 129.
The DBR semiconductor laser includes an active region for obtaining a gain and the DBR region for controlling the oscillation wavelength. The DBR region is made of a material having a band gap larger than that of the active region so that the DBR region is transparent for the laser light with a wavelength of 850 nm. Since the DBR region has a lattice, the oscillation wavelength is controlled by the wavelength of the light reflected from the DBR region.
Thus, the oscillation wavelength can be varied by varying the refractive index of the DBR region. The refractive index of the DBR region can be varied by methods such as (1) supplying a current to the DBR region, and (2) varying the temperature of the semiconductor laser using an electronic cooling element (Peltier element) and the like.
However, in the case of varying the oscillation wavelength by varying the DBR current, it may difficult to precisely fix the oscillation wavelength at a desired value.
On the other hand, in the case of varying the oscillation wavelength by varying the temperature of the semiconductor laser, an electronic cooling element having a heat absorption capacitance of about 1 W is required for the control of the temperature of the semiconductor laser, which increases power consumption. Moreover, when the ambient temperature under which the semiconductor laser is used becomes wider, operational reliability may be deteriorated. In addition, output intensity of laser light varies as the temperature of the semiconductor laser varies for changing the oscillation wavelength. If the current supplied to the active region is adjusted to compensate the output variation, the phase condition changes, causing mode hopping.
In order to avoid the mode hopping, a semiconductor laser having a phase control section has been proposed. However, it is likely to be difficult to find a control method for stably and continuously varying the oscillation wavelength irrespective of a variation of the ambient temperature.
In the short-wavelength light source including the semiconductor laser having the DBR region and the wavelength converting device, it is required to match the oscillation wavelength of the semiconductor laser with the phase-matching wavelength of the wavelength converting device. In the short-wavelength light source, the output of short-wavelength light varies if the oscillation wavelength shifts from the phase-matching wavelength. In particular, when a quasi-phase matching (QPM) type wavelength converting device having a periodic domain inverted structure is used as the wavelength converting device, it is significantly important to control the oscillation wavelength of the semiconductor laser because the allowance for the phase-matching wavelength is as narrow as about 0.1 nm.
Another problem of the short-wavelength light source is that LiTaO3 crystal and LiNbO3 crystal used for the substrate of the OPM type device have optical damage characteristics. The optical damage as used herein refers to the variation of the refractive index caused by irradiation with short-wavelength light. As the refractive index varies, the phase-matching wavelength of the QPM type device shifts. In order to obtain a stable harmonic output, therefore, it is required to always control the wavelength of the semiconductor laser to match with the phase-matching wavelength.
A light generating apparatus of the present invention includes: a submount; a semiconductor laser chip mounted on the submount; a substrate which is mounted on the submount and includes an optical waveguide; and a substance having a predetermined thickness which is disposed between the semiconductor laser chip and the substrate.
Preferably, the substrate is a ferroelectric crystal substrate. The ferroelectric crystal substrate may include LiTaxNb1xe2x88x92xO3 (0xe2x89xa6xc3x97xe2x89xa61). A periodic domain inverted structure formed on the ferroelectric substrate may further be included.
The optical waveguide may be formed by an ion-exchange technique.
In one embodiment, the substance is a glass ball. Alternatively, the substance can be an optical fiber.
According to another aspect of the invention, a light generating apparatus includes: a submount including a first surface and a second surface; a semiconductor laser chip mounted on the first surface of the submount; and a substrate which is mounted on the second surface of the submount and includes an optical waveguide, wherein the first surface and the second surface are positionally perpendicular to each other.
Preferably, the substrate is a ferroelectric crystal substrate. The ferroelectric crystal substrate may include LiTaxNb1xe2x88x92xO3 (0xe2x89xa6xc3x97xe2x89xa61). A periodic domain inverted structure formed on the ferroelectric substrate may be further included.
The optical waveguide may be formed by an ion-exchange technique.
According to still another aspect of the invention, a light generating apparatus includes: a submount including a first portion and a second portion; a semiconductor laser chip mounted onto the first portion of the submount; and a substrate which is mounted onto the second portion of the submount and includes an optical waveguide, wherein material constituting the first portion is different from material constituting the second portion.
Preferably, the substrate is a ferroelectric crystal substrate. The ferroelectric crystal substrate may include LiTaxNb1xe2x88x92xO3 (0xe2x89xa6xc3x97xe2x89xa61). A periodic domain inverted structure formed on the ferroelectric substrate may be further included.
The optical waveguide may be formed by an ion-exchange technique.
In one embodiment, a crystal thin plate having birefringence which is disposed between the first portion and the second portion of the submount is further provided.
Preferably, a thermal conductivity of the first portion is larger than that of the second portion.
In one embodiment, the first portion and the second portion are made of a ceramic.
According to still another aspect of the invention, a method for fabricating a light generating apparatus includes the steps of: forming an alignment marking on each of a submount, a semiconductor laser chip and a substrate, the submount including a first surface and a second surface which are positionally perpendicular to each other, and the substrate including an optical waveguide; aligning the submount and the semiconductor laser chip using the alignment markings on the submount and the semiconductor laser chip to mount the semiconductor laser chip on the first surface of the submount; and aligning the submount and the substrate using the alignment markings on the submount and the substrate to mount the substrate on the second surface of the submount.
Preferably, the substrate is a ferroelectric crystal substrate. The ferroelectric crystal substrate may include LiTaxNb1xe2x88x92xO3 (0xe2x89xa6xc3x97xe2x89xa61). The method may further include the step of providing a periodic domain inverted structure on the ferroelectric substrate.
The method may further includes the step of forming the optical waveguide by an ion-exchange technique.
According to still another aspect of the invention, a method for fabricating a light generating apparatus includes the steps of: forming an alignment marking on each of a submount and a semiconductor laser chip, the submount including a first surface and a second surface; irradiating a surface of the submount opposite to the first surface with light which is allowed to pass through the submount, and respectively identifying an image of the alignment marking on each of the submount and the semiconductor laser chip; aligning the submount and the semiconductor laser chip using the alignment markings on the submount and the semiconductor laser chip to mount the semiconductor laser chip on the first surface of the submount; and mounting a substrate including an optical waveguide onto the second surface of the submount.
The light may be a laser light emitted from an InP type semiconductor laser.
Preferably, the substrate is a ferroelectric crystal substrate. The ferroelectric crystal substrate may include LiTaxNb1xe2x88x92xO3 (0xe2x89xa6xc3x97xe2x89xa61). The method may further include the step of providing a periodic domain inverted structure on the ferroelectric substrate.
The method may further include the step of forming the optical waveguide by an ion-exchange technique.
According to still another aspect of the invention, a method for fabricating a light generating apparatus includes the steps of: allowing at least a portion of a layered structure for laser oscillation in a semiconductor laser chip to emit light so as to form a light emitting region; identifying the light emitting region of the semiconductor laser chip to obtain a positional information of the semiconductor laser chip, and mounting the semiconductor laser chip at a predetermined position on a submount based on the positional information; and mounting a substrate on the submount, the substrate including an optical waveguide.
In one embodiment, the light emitting region is formed by optical excitation. In another embodiment, the light emitting region is formed by coupling external light to an active layer of the semiconductor laser chip. In still another embodiment, the light emitting region is formed by pulse-driving the semiconductor laser chip.
Preferably, the substrate is a ferroelectric crystal substrate. The ferroelectric crystal substrate may include LiTaxNb1xe2x88x92xO3 (0xe2x89xa6xc3x97xe2x89xa61). The method may further include the step of providing a periodic domain inverted structure on the ferroelectric substrate.
The method may further include the step of forming the optical waveguide by an ion-exchange technique.
According to still another aspect of the invention, a light generating apparatus includes: a submount; a semiconductor laser chip mounted on the submount; and a substrate which is mounted on the submount and includes a plurality of optical waveguides, herein a surface of the substrate at which the optical waveguides are formed and a surface of the submount onto which the substrate is mounted are in a non-parallel relationship.
In one embodiment, a projection formed on the surface of the substrate at which the optical waveguides are formed is further included, the projection providing the non-parallel relationship.
In another embodiment, a projection formed on the surface of the submount on which the substrate is mounted is further included, the projection providing the nonparallel relationship.
In still another embodiment, the substrate includes a top surface and a bottom surface which are not in parallel with each other, thereby providing the nonparallel relationship.
Preferably, the substrate is a ferroelectric crystal substrate. The ferroelectric crystal substrate may include LiTaxNb1xe2x88x92xO3 (0xe2x89xa6xc3x97xe2x89xa61). A periodic domain inverted structure formed on the ferroelectric substrate may be further included.
The optical waveguide may be formed by an ion-exchange technique.
According to still another aspect of the present invention, provided is a method for fabricating a light generating apparatus includes: a submount; a semiconductor laser chip; and a substrate including an optical waveguide, wherein a surface of the substrate on which the optical waveguide is formed and a surface of the submount onto which the substrate is mounted are in a non-parallel relationship with each other. The method includes the steps of: processing at least one of the submount and the substrate to obtain the non-parallel relationship; mounting the semiconductor laser chip on the submount; and moving the substrate on the submount in a direction parallel with an optical axis of the mounted semiconductor laser chip to adjust an optical coupling between the substrate and the semiconductor laser chip in a direction of a thickness of the substrate, and mounting the substrate at a predetermined position on the substrate.
In one embodiment, the method may further include the step of forming a projection on the surface of the substrate on which the optical waveguides are formed, the projection providing the non-parallel relationship.
In another embodiment, the method may further include the step of forming a projection on the surface of the submount on which the substrate is mounted, the projection providing the non-parallel relationship.
In still another embodiment, the method may further include the step of making a top surface and a bottom surface of the substrate unparallel with each other, thereby providing the non-parallel relationship.
Preferably, the substrate is a ferroelectric crystal substrate. The ferroelectric crystal substrate may include LiTaxNb1xe2x88x92xO3 (0xe2x89xa6xc3x97xe2x89xa61). The method may further include the step of providing a periodic domain inverted structure on the ferroelectric substrate.
The method may further include the step of forming the optical waveguide by an ion-exchange technique.
According to still another aspect of the present invention, provided is an oscillation wavelength stabilizing apparatus for a light source, wherein the light source is a semiconductor laser, includes: an active region for providing gain; and a distributed Bragg reflection (DBR) region for controlling an oscillation wavelength. The apparatus includes a control section which monotonously varies, in a first direction, a DBR current to be input to the DBR region while detecting the oscillation wavelength of an output light of the semiconductor laser so as to detect a DBR current value Io corresponding to a predetermined oscillation wavelength value, and then monotonously varies the DBR current in a second direction which is opposite the first direction beyond the detected value Io, and then monotonously varies the DBR current in the first direction again to set the DBR current at the detected value Io, thereby fixing the oscillation wavelength of the semiconductor laser at the predetermined oscillation wavelength value.
In one embodiment, the control section provides a different input rate of the DBR current into the DBR region between a range of the DBR current in which the oscillation wavelength continuously changes and a range of the DBR current in the vicinity of a current level at which mode-hopping occurs.
In another embodiment, the detected value Io of the DBR current is set so as to satisfy equation Io=(I1+I2)/2 where I1 is a first DBR current value at which mode-hopping occurs and I2 is an adjacent DBR current value at which mode-hopping occurs.
According to still another aspect of the present invention, provided is an oscillation wavelength stabilizing apparatus for a light source, wherein the light source is a semiconductor laser includes: an active region for providing gain; a distributed Bragg reflection (DBR) region for controlling an oscillation wavelength; and an electronic cooling element. The apparatus includes a control section which varies a DBR current to be input to the DBR region to set an oscillation wavelength of an output light of the semiconductor laser in the vicinity of a predetermined oscillation wavelength value, and then allows a temperature of the semiconductor laser to vary by the electronic cooling element, thereby fixing the oscillation wavelength of the semiconductor laser at the predetermined oscillation wavelength value.
Preferably, in an initial setting process, the control section may set the temperature of the semiconductor laser in the vicinity of ambient temperature.
According to still another aspect of the present invention, provided is as oscillation wavelength stabilizing apparatus for a light source, wherein the light source is a semiconductor laser including: an active region for providing gain; a distributed Bragg reflection (DBR) region for controlling an oscillation wavelength; and an electronic cooling element. The apparatus includes a control section which allows a temperature of the semiconductor laser to vary by the electronic cooling element to vary the oscillation wavelength of the semiconductor laser, and further causes the DBR current to be input to the DBR region to be varied, thereby compensating for a phase change of the semiconductor laser.
In one embodiment, the control section further adjusts a current to be input to the active region in response to a change in an output of the semiconductor laser.
According to still another aspect of the present invention, provided is as oscillation wavelength stabilizing apparatus for a light source, wherein the light source is a semiconductor laser including: an active region for providing gain; a distributed Bragg reflection (DBR) region for controlling an oscillation wavelength; a phase control region; and a temperature sensor. The apparatus includes:a first control circuit for adjusting a current to be input to the active region so as to maintain a uniform output of the semiconductor laser; a second control circuit for adjusting a DBR current to be input to the DBR region so as to set the oscillation wavelength of the semiconductor laser at a predetermined oscillation wavelength value; and a third control circuit for adjusting a current to be input to the phase control region so as to compensate for a phase change detected by the first control circuit, the second control circuit, and the temperature sensor.
According to still another aspect of the present invention, provided is an oscillation wavelength stabilizing apparatus for a light source, wherein the light source is a semiconductor laser including: an active region for providing gain; a distributed Bragg reflection (DBR) region for controlling an oscillation wavelength; and a phase control region. The apparatus includes a control section which allows a DBR current to be input to the DBR region to vary in a initial setting process so as to set the oscillation wavelength of the semiconductor laser in the vicinity of a predetermined oscillation wavelength value, and then varies both a current to be input to the phase control region and the DBR current, thereby fixing the oscillation wavelength of the semiconductor laser at the predetermined oscillation wavelength value.
According to still another aspect of the present invention, provided is a harmonic output stabilizing apparatus for a light source, wherein the light source is a short wavelength light source including: a semiconductor laser including an active region for providing gain and a distributed Bragg reflection (DBR) region for controlling an oscillation wavelength; and a wavelength converting device made of non-linear optical crystal. The apparatus includes a control section which monotonously varies, in a first direction, a DBR current to be input to the DBR region while detecting a harmonic optical output of the short wavelength light source so as to detect a DBR current value Io corresponding to a monotonously varies the DBR current in a second direction which is opposite the first direction beyond the detected value Io, and then monotonously varies the DBR current in the first direction again to set the DBR current at the detected value Io, thereby fixing the oscillation wavelength of the semiconductor laser at a phase-matching wavelength of the wavelength converting device.
According to still another aspect of the present invention, provided is a harmonic output stabilizing apparatus for a light source, wherein the light source is a short wavelength light source including: a semiconductor laser including an active region for providing gain and a distributed Bragg reflection (DBR) region for controlling an oscillation wavelength; a wavelength converting device made of non-linear optical crystal; and an electronic cooling device, the apparatus comprising a control section which varies a DBR current to be input to the DBR region to set an oscillation wavelength of an output light of the semiconductor laser in the vicinity of a phase-matching wavelength of the wavelength converting device, and then allows a temperature of the short wavelength light source to vary by the electronic cooling element, thereby fixing the oscillation wavelength of the semiconductor laser at the phase-matching wavelength of the wavelength converting device.
In one embodiment, in an initial setting process, the control section sets the temperature of the semiconductor laser in the vicinity of an ambient temperature.
According to still another aspect of the present invention, provided is a harmonic output stabilizing apparatus for a light source, wherein the light source is a short wavelength light source including: a semiconductor laser including an active region for providing gain and a distributed Bragg reflection (DBR) region for controlling an oscillation wavelength; a wavelength converting device made of a non-linear optical crystal; and an electronic cooling element. The apparatus includes a control section which allows a temperature of the short wavelength light source to vary by the electronic cooling element to vary the oscillation wavelength of the semiconductor laser toward a phase-matching wavelength of the wavelength converting device, and further causes a DBR current to be input to the DBR region to be varied, thereby compensating for a phase change of the semiconductor laser.
In one embodiment, the control section further adjusts a current to be input to the active region in response to a change in an output of the semiconductor laser.
According to still another aspect of the present invention, provided is a harmonic output stabilizing apparatus for a light source, wherein the light source is a short wavelength light source including: a semiconductor laser including an active region for providing gain, a distributed Bragg reflection (DBR) region for controlling an oscillation wavelength, a phase control region and a temperature sensor; and a wavelength converting device made of a non-linear optical crystal. The apparatus includes: a first control circuit for adjusting a current to be input to the active region so as to maintain a uniform output of the semiconductor laser; a second control circuit for adjusting a DBR current to be input to the DBR region so as to set the oscillation wavelength of the semiconductor laser at a phase-matching wavelength of the wavelength converting device; and a third control circuit for adjusting a current to be input to the phase control region so as to compensate for a phase change detected by the first control circuit, the second control circuit, and the temperature sensor.
According to still another aspect of the present invention, provided is a harmonic output stabilizing apparatus for a light source, wherein the light source is a short wavelength light source including: a semiconductor laser including an active region for providing gain, a distributed Bragg reflection (DBR) region for controlling an oscillation wavelength and a phase control region; and a wavelength converting device made of a nonlinear optical crystal. The apparatus includes a control section which allows a DBR current to be input to the DBR region to vary in an initial setting process so as to set the oscillation wavelength of the semiconductor laser in the vicinity of a phase-matching wavelength of the wavelength converting device, and then varies both a current to be input to the phase control region and the DBR current, thereby fixing the oscillation wavelength of the semiconductor laser at the phase-matching wavelength of the wavelength converting device.
In one embodiment, the wavelength converting device is a quasi-phase-matching type wavelength converting device having a periodic domain inverted structure. In another embodiment, the wavelength converting device is an optional waveguide type wavelength converting device. The wavelength converting device may be a bulk type wavelength converting device.
The non-linear optical crystal may include LiTaxNb1xe2x88x92xO3 (0xe2x89xa6xc3x97xe2x89xa61).
According to still another aspect of the present Invention, an optical disk system includes a short wavelength light source including: a semiconductor laser including an active region for providing gain and a distributed Bragg reflection (DBR) region for controlling an oscillation wavelength; and a wavelength converting device made of a non-linear optical crystal which is integrated with the semiconductor laser. An output light from the short wavelength light source scans an optical disk to conduct at least one of a recording operation and a reproducing operation for a signal. The optical disk system further includes a control section for re-controlling the oscillation wavelength of the semiconductor laser at a phase-matching wavelength of the wavelength converting device during a predetermined period in a system operation.
In one embodiment, the predetermined period is a standby period of the system.
In another embodiment, the predetermined period is at least one of a transition period from the reproducing operation to the recording operation and a seek period at a transition from the recording operation to the reproducing operation,
In still another embodiment, a memory is further provided or storing a reproduced signal, wherein during the predetermined period, a harmonic output of the short wavelength light source is varied and the signal stored in the memory is used.
In still another aspect of the present invention, a memory is further provided for storing a reproduced signal, wherein during the predetermined period, the memory is full with the stored signal with a signal-storing rate being larger than a signal-readout rate, and the signal stored in the memory is used.
In still another embodiment, a system may further include an electronic cooling element integrated with the short wavelength light source, wherein the control section re-adjusts a temperature of the short wavelength light source in the vicinity of an ambient temperature using the electronic cooling element, and varies a DBR current to be input to the DBR region, thereby re-adjusting the oscillation wavelength of the semiconductor laser at the phase-matching wavelength of the wavelength converting device.
In still another aspect of the present invention, the semiconductor laser further includes a phase control region, and the control section resets a current to be input to the phase control section, and varies both the current to be input to the phase control region and a current to be input to the DBR region, thereby re-adjusting the oscillation wavelength of the semiconductor laser at the phase-matching wavelength of the wavelength converting device.
In one embodiment, the wavelength converting device is a quasi-phase-matching type wavelength converting device having a periodic domain inverted structure. In another embodiment, the wavelength converting device is an optical waveguide type wavelength converting device. In still another embodiment, the wavelength converting device is a bulk type wavelength converting device.
The
non-linear optical crystal may include LiTaxNb1xe2x88x92xO3 (0xe2x89xa6xc3x97xe2x89xa61).
Thus, the invention described herein makes possible the advantages of (1) providing a small light generator including a semiconductor laser and a waveguide type optical functional device where alignment adjustment for obtaining optical adjustment therebetween can be easily performed, (2) providing the method for producing the same, (3) providing an oscillation wavelength stabilizer for a semiconductor laser having a DBR region capable of performing stable oscillation wavelength control, (4) providing a harmonic output stabilizer capable of providing stable short-wavelength light output, and (5) providing an optical disk system including such a harmonic output stabilizer.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.